A hard disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces. When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head that is positioned over a specific location of a disk by an actuator.
A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. Write heads make use of the electricity flowing through a coil, which produces a magnetic field. Electrical pulses are sent to the write head, with different patterns of positive and negative currents. The current in the coil of the write head induces a magnetic field across the gap between the head and the magnetic disk, which in turn magnetizes a small area on the recording medium.
An HDD includes at least one head gimbal assembly (HGA) that generally includes a slider that houses the head, and a suspension. Each slider is attached to the free end of a suspension that in turn is cantilevered from the rigid arm of an actuator. Several semi-rigid arms may be combined to form a single movable unit, a head stack assembly (HSA), having either a linear bearing or a rotary pivotal bearing system. The suspension of a conventional disk drive typically includes a relatively stiff load beam with a mount plate at the base end, which subsequently attaches to the actuator arm, and whose free end mounts a flexure that carries the slider and its head. It is the job of the flexure to provide gimbaled support for the slider so that the read/write head can pitch and roll in order to adjust its orientation.
The flexure in an integrated lead suspension is generally made out of a laminated multilayer material. Typically, it consists of a support layer (e.g., steel), a dielectric insulating layer (e.g., polyimide), a conductor layer (e.g., copper), and a cover layer (e.g., polyimide) that insulates the conductor layer. The electrical lead lines are etched into the conductor layer, while the polyimide layer serves as the insulator from the underlying steel support layer. The steel support layer is also patterned to provide strength and gimbaling characteristics to the flexure. The conducting leads, called traces, which electrically connect the head transducer to the read/write electronics, are often routed on both sides of the suspension, especially in the gimbal region. Normally the traces consist of copper conductor with polyimide dielectric insulating and cover layers but no support stainless steel layer and only provide the electrical function. The primary mechanical support function is provided by the flexure legs (e.g., steel) which normally run adjacent to the traces.
Increasing areal density (a measure of the quantity of information bits that can be stored on a given area of disk surface) is one of the ever-present holy grails of hard disk drive design evolution, and has led to the necessary development and implementation of secondary and even tertiary actuators for improved head positioning through relatively fine positioning, in addition to a primary voice coil motor (VCM) actuator which provides relatively coarse positioning. Some hard disk drives employ micro- or milli-actuator designs to provide second stage actuation of the recording head to enable more accurate positioning of the head relative to the recording track. Milli-actuators are broadly classified as actuators that move the entire front end of the suspension: spring, load beam, flexure and slider. Micro-actuators are broadly classified as actuators that move only the slider, moving it relative to the load beam, or moving the read-write element only, moving it relative to the slider body.
Piezoelectric (PZT) based and capacitive micro-machined transducers are two types of microactuators that have been proposed for use with HDD sliders. The microactuators need to be mechanically and electrically coupled to flexure support structure, with very limited mechanical tolerances, such as by using an electrically conductive adhesive. Thus, undesirable electrical shorts may occur which are associated with this microactuator assembly process. Further, because manufacturing yield is typically a fundamental design and manufacturing goal, eliminating or minimizing electrical shorts is desirable.